My standard brief when I am getting checked-out in a new aircraft is to say to the instructor "In the event of an engine failure or other emergency, I will say 'You have control'"
Mine is slightly different. I expect to have first go at handling most emergencies but I will say:
"In the event of fire, I will say 'You have control'"
In fact the only time I've had an emergency, on a joyride with an instructor in foreign parts, he took control before I could get my mouth open.